The operator of an over-the-road truck is often required to remain in the driver's seat through substantially the whole of a working day that may be long and trying. For such an operator, seating comfort is more than a mere convenience, inasmuch as the fatigue that results from occupying an uncomfortable seat can have a direct bearing upon the safety with which the vehicle is operated and possibly upon the long-term health of the operator.
Until comparatively recent years, it was not customary to provide arm-rests on the drivers' seats of over-the-road trucks or the operators' seats of other highway and off-highway vehicles; but with increased awareness of the need for seating comfort, it has come to be recognized that arm-rests are useful both for supporting the upper arms to minimize shoulder muscle fatigue and for supporting the torso against side sway. To be fully effective for the performance of both of these functions, the arm-rests should be adjustable in height, so that their positions can be accommodated to the physical dimensions of the seat occupant.
Furthermore, heightwise adjustment of the arm-rests should be very easily accomplished so that the seat occupant can provide for an occasional change in position without having to divert his attention from operation of the vehicle. For quick and easy arm-rest adjustment, the seat occupant should not have to fumble for a push button, release lever or the like. On the other hand, there should not be any projecting parts on the arm-rest adjusting mechanism that can catch on clothing or otherwise present a hazard to the occupant of a moving vehicle.
It should also be kept in mind that a person usually gets into and out of a vehicle seat from one side of it, and that an arm-rest in its normal position would be in the way of entry to the seat and departure from it. It is therefore especially important in the case of a vehicle seat that the arm-rest be quickly and easily movable to an out-of-the-way position.
The problem of providing a vehicle seat arm-rest with a substantial range of heightwise adjustment (e.g., on the order of eight to ten inches vertically) does not have an obvious solution. The arm-rest cannot very well be confined to vertical motion by means of fixed, upright guide means on the seat frame because such guide means would either project above the arm-rest when it was in the lower part of its range of positions or would limit the range of adjusting vertical motion of the arm-rest proper. The problem is further complicated by the need to provide for vertical adjustment and tilting reorientation of the arm-rest in accordance with the requirements outlined above.